| The Electromagnetic Acoustic Transducer(EMAT)is widely used in the field of non-destructive testing,because of its non-contact,high precision,suitable for high temperature and high speed detection and easy to emit ultrasonic waves of various types.Theorical and experimental investigation on electromagnetic ultrasonic guided wave testing are conducted in this dissertation.(1)The basic theory of electromagnetic ultrasonic guided wave detection was studied,and the detection method of electromagnetic ultrasonic guided wave was analyzed in this paper.On the basis of the theoretical research,the Lamb waveguide EMAT was optimized and the multi-split transducer coil and new permanent magnet structure were designed.The simulation of Lamb wave EMAT was accomplished by using finite element simulation software COMSOL Multiphysics,including the eddy current density distribution of coil,Lorentz force distribution,and magnetic flux density distribution of permanent magnets,etc.,and the analysis and verification experiments were carried out.(2)The hardware circuit of electromagnetic ultrasonic guided wave detection system was designed,made and tested,including the excitation device composed of the control circuit,the boost circuit,the driving circuit and the power amplifier circuit,and the receiving device composed of low noise preamplifier,broadband amplifier and analog low pass filter,and the performance of each module was tested.(3)The experimental platform of electromagnetic ultrasonic guided wave detection system was set up.The signal characteristics of the ultrasonic guided wave were analyzed.The defects of the aluminum plate were detected by using Lamb waveguide,and the amplitude of the received signal was improved by using the parallel tuning capacitance of the receiving coil. |
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